DESCRIPTION: Chitin plays a crucial role in the physiology of the vast majority of infectious fungi. Chitin synthase (CS) is the enzyme responsible for chitin biosynthesis, and CS is thus a common denominator uniting these organisms. The enzyme is absent in vertebrate animals, and represents an attractive target for selective service therapeutic intervention in parasitic diseases. The successful development of a potent CS inhibitor would have application to a number of wide-spread human ailments, and would represent a general approach to the inhibition of other biologically relevant processive glycosyl transferases. The proposed approach to the development of new CS inhibitors is based on two relatively recent developments. The first of these is the emergence of hydrophobic cluster analysis (HCA) as a widely-used and widely-accepted computational method for identifying structural similarities between proteins with known genetic sequences. HCA of a number of processive glycosyl transferases such as chitin synthase suggests that they process two equivalents of UDP-sugar simultaneously. This in turn suggests that bisubstrate analogs which mimic two equivalents of UDP-GlcNAc should distinguish CS from the numerous mammalian UDP-GlcNAc-dependent glycosyl transferases. The second development upon which this proposal relies is the collection of technical advances commonly referred to as combinatorial chemistry. This set of techniques has made it possible to consider the parallel synthesis and screening of hundred or thousands of potential lead structures rather than the serial synthesis of a much smaller number of compounds by traditional methods. In the present case, where very little is known about the enzyme, combinatorial synthesis offers the opportunity to ask thousands of questions (each represented by a molecule) about the structure of the active site simultaneously. Provided the pool of questions is well chosen, it will be possible to rapidly identify high affinity ligands for CS. This process will simultaneously provide mechanistic information about enzyme, define a general approach to the inhibition of processive glycosyl transferases, and chart the path towards new inhibitors and (eventually) new therapeutic agents.